1. Field of the Invention
The present invention relates to a surface-modified insulator and a method of surface-modifying an insulator with a fluoroorganosilane- and/or siloxane-containing preparation
2. Discussion of the Background
Insulators are widely employed throughout industry, for example, as high-tension insulators in transformer stations or in transmission lines. These insulators must meet exacting technical requirements for as long as possible under onerous service conditions, in particular under the stress caused by contamination layers of dirt, salt or other deposits.
A contamination layer deposited on the surface of the insulator impairs the electrical insulation capacity. Countermeasures against the effects of such contamination include complex constructional forms with high shield spread and long leakage paths. In addition, heavily contaminated surfaces require manual cleaning at regular intervals.
From xe2x80x9cElektrotechnische Zeitschriftxe2x80x94Axe2x80x9d, 96 (1995), pages 126 to 128, it is also known to apply a hydrophobic coating of silicone to the surface of an insulator. The insulator surface consequently repels water, thereby avoiding the buildup of a contamination layer by water-dissolved particles. Because of the thus-imparted hydrophobic characteristics, an insulator soiled with a contamination layer retains its electrical properties, since coherent films of water, or moisture zones, are unable to form, and the service life of the insulator is thus extended. A disadvantage, however, is that such siliconization of the surface is not permanent and must be renewed from time to time. This entails a high maintenance effort and an expensive plant shutdown. Moreover, the silicone material required for the hydrophobic coating is expensive.
EP 0 497 189 B1 discloses a process for preparing a water- and oil-repellent adsorbed film in which a substrate having a pre-roughened surface and having active hydrogen groups thereon is contacted with a nonaqueous solution of a surface-active material. The active material contains a fluorocarbon group and a chlorosilyl group or a fluorocarbon group and an alkoxy group. The solvents employed in this method are chlorohydrocarbons, which are at present comparatively expensive and extremely toxic. The application examples mentioned in the reference include high-tension insulators and sparkplugs. However, as noted above, a coating of this type is not permanent under onerous service conditions, since the attachment of coating to the insulator is inadequate.
It is also known to prepare a composition that contains an organofluorine-functional siloxane by controlled acid- or base-regulated hydrolysis and condensation or co-condensation of organofluorine-functional chlorosilanes and/or alkoxysilanes with or without additional precursor components. The pH regulators employed in this case include not only organic or inorganic acids or bases but also acidic or basic salts, such as alkali metal carbonate, alkali metal hydrogen sulfate, alkali metal dihydrogen phosphate, magnesium hydroxide and aluminum acetate. In preparing such a composition it is also known to employ, for example, silicon tetrachloride or else titanium tetrachloride or zirconium tetrachloride, or corresponding metal acid esters, as precursor components.
Such water, solvent- or dispersant-containing compositions are generally employed for the hydrophobic and simultaneously oleophobic and dirt-repellent treatment of substrates or for special modification of the surface properties of the substrates; for example, for the surface treatment of metals, metal oxides, fillers, pigments, glass, enamel, ceramic, building materials, buildings, fibers, textiles, natural substances, plastics, and coating materials. The surface modification may also involve the formation of a protective layer against UV radiation or mechanical, thermal and chemical influences. It is therefore possible, for example, to obtain scratch-resistant, anticorrosive, antiicing, antifouling, antibacterial or antithrombic properties. In addition to the organofunctional groups, the above-noted organofluorine-functional siloxanes generally possess Si-bonded hydroxyl and/or alkoxy groups, which are intended to permit subsequent attachment to the substrate. Here again, however, no satisfactory, i.e., permanent attachment of the coating to the substrate is achieved.
Fluoroalkylsilanes are used in accordance with EP 0 382 557 A1 to coat the surface of inorganic packings which are in turn dispersed in an insulating high-polymer material for the production of water-repellent dielectric materials. Such a procedure is generally very complex and cannot be applied to the modification of the entire surface of workpieces, especially those of glass or ceramic.
It is therefore an object of the present invention to provide an insulator with a water-, oil-, and dirt-repellent coating having satisfactory adhesion properties.
It is another object of the invention to provide a method for modify the surface of an insulator by means of which the coating can be easily produced.
Yet another object of the invention is to specify a preparation for use in the method and by means of which the coating can be produced.
These and other objects are achieved in accordance with the invention by the present invention, the first embodiment of which provides a surface-modified insulator, that includes:
an insulator body having a coating on at least a portion thereof prepared from a composition including:
at least one organofluorine-functional silane, organofluorine-functional siloxane, or a mixture thereof,
at least one mineral acid; and
at least one metal salt of a metal selected from the group consisting of aluminum(III), tin(II), tin(IV), iron(III) or titanium(III)
Another embodiment of the invention provides a method of modifying the surface of an insulator, which includes applying to at least a portion of a body of the insulator a coating prepared from a composition including:
at least one organofluorine-functional silane, organofluorine-functional siloxane, or a mixture thereof;
at least one mineral acid; and
at least one metal salt of a metal selected from the group consisting of aluminum(III), tin(II), tin(IV), iron(III) or titanium(III).
Another embodiment of the invention provides an insulator body coating composition, that includes:
at least one organofluorine-functional silane, organofluorine-functional silane, or a mixture thereof;
at least one mineral acid; and
at least one metal salt of a metal selected from the group consisting of aluminum(III), tin(II), tin(IV), iron(III) or titanium(III).